1. Field of the Invention
The present invention relates to a system for driving a display device utilizing liquid crystals, and, more particularly, a system capable of increasing remarkably the service life of the crystal liquid used in the display device. The system for driving a liquid crystal display device in accordance with the present invention is especially effective for application to large scale integrated circuit devices.
2. Description of the Prior Art
In the past, DC or pulse driving systems have been used for driving liquid crystal display devices. The service life of the liquid crystal used in the display devices is greatly dependent on voltage and current applied thereto. Even when a driving voltage is used which is less than a breakdown voltage of the liquid crystal, to drive the display device without changing the polarity, the composition of the liquid crystal is changed when such voltage is applied for a long time so that it gradually degenerates in function. For example, in a liquid crystal display device utilizing the nematic liquid crystal whose major portion is anisylidenepara-amino-phenyl-acetate (APAPA), in which the total thickness of the liquid crystal is of the order of 25 microns, the contrast ration, that is the difference in light transmission between a portion to which the voltage is applied and a portion to which no voltage is applied, is increased as the applied DC current is increased. For example, the reflection contrast is saturated at 40- 50 volts. Therefore, a high voltage cannot be applied in the case of a dynamic display. Furthermore when the DC voltage is applied, the service life of the crystal becomes very short, and craters and blurs are produced in hundreds of hours.
One of the objects of the present invention is therefore to provide an improved system for driving a liquid crystal display device.
Another object of the present invention is to provide a system for driving a liquid crystal display device in which the liquid crystal is driven not by direct current, but by alternating current, thereby increasing the service life of the liquid crystal.
Another object of the present invention is to provide a system for driving a liquid crystal display device which is simple in construction and capable of utilizing as a power source a residential electric distribution line source.
Another object of the present invention is to provide a system for driving a liquid crystal display device which is adapted for dynamic display.
Another object of the present invention is to provide a system for driving a liquid crystal display device especially adapted for use with large scale integrated circuit devices whose elements are MOS-FET or metal oxide semiconductor field-effect transitors.